Twin Analog Devices 24-Bit DACs: The Cambridge Audio 851D
employs two very high-quality Analog Devices (AD1955) 24-bit DACs in
dual-differential mode for superior sound-staging and stereo imaging. Since each
channel has its own DAC to process information, completely separate and
symmetrical analog filter circuitry can be implemented. This implementation
allows both the left- and right-channel circuitry to operate identically,
ensuring the 851D delivers fantastic sound-staging and stereo-imaging
ATF2 (Adaptive Time Filtering) Upsampling: All stereo
sources can be upsampled to 24-bit/384kHz and kept jitter-free by proprietary,
second generation ATF Adaptive Time Filtering algorithms co-developed with
Anagram Technologies of Switzerland. ATF2 Upsampling allows digital audio
signals from virtually any audio source to be upsampled, resynchronised, and
retimed for extraordinary levels of detail. In effect, upsampling the digital
data stream (up to 24-bit/384kHz) allows your digital music files (from
MP3 to high-resolution downloads) to have the enhanced audio clarity, richness
and dynamic range that would normally be associated with SACD or DVD-Audio
discs. Three proprietary technologies are included in ATF2 effectively reduce
noise artifacts caused by imperfect digital systems and allow the digital signal
to closer represent the true analog sound of the studio mastered audio data.
- Adaptive Time Filtering: Adaptive time filtering allows
the system to adapt to small fluctuations in the systems audio master clock.
The master clock is the heart of any digital audio system, however as all
components that are constructed from physical materials, they will at some
point in time deviate from their ideal generalized behavior causing, in this
case variation in frequency and system jitter in this important internal
timing reference. Typically these variations will not be corrected for,
however in ATF2 enabled devices the system automatically adapts to these
small fluctuations resulting in perfect "glitch" free analog sound even
after endless hours of continuous playback.
- Jitter Suppression: Jitter Suppression allows any
incoming audio stream to be resynchronised and retimed to a local very high
quality clock. By using a stable-reference oscillator, the negative effects
of inter-component jitter can be dramatically reduced. When converting the
digital audio to an analogue signal through high performance D/A converters,
this reduction in jitter has enormous benefits in the level of detail and
clarity in the reconstructed analogue sound.
- Time Domain Model: Combining this process with a time
domain model using an advanced cubic interpolation algorithm, the unique
ATF2 system upsamples all incoming audio to 24 bits at 384kHz whilst
applying noise shaped dither and is able to actually increase the linearity
of response of the D/A converters. The end result is tighter, more focused
bass, increased stereo imaging, focus and separation for all musical
instruments and voices.
Phase Filter Select: The 851D's ATF2 Upsampling technology
employs Cambridge Audio's own proprietary digital filter algorithms with three
different filter options available - Linear Phase, Minimum Phase, and Steep.
Controlled from one switch on the front-panel, they are extremely clever
audiophile topologies specifically developed for audio playback and all offer
excellent sound quality, but differ slightly to appeal to a wide range of
- Linear Phase Filter: The Linear Phase Filter uniquely
features "constant group delay" which delays all audio signals at all
frequencies by the same amount, meaning all audio is fully time-coherent at
- Minimum Phase Filter: The Minimum Phase Filter does not
feature constant group delay, but rather has been optimized without
feed-forward so that the impulse response exhibits no pre-ringing in the
time domain. Many audiophiles have argued that the pre-ringing, as seen in
nearly all digital filter designs, may affect the transient attack of
percussive instruments. Minimum phase implementation eliminates
- Steep Filter: The steep filter removes
undistinguishable artifacts via re-calibration for a very slight roll-off at
20kHz, but an ultra-steep drop to the stop-band just after 20kHz.
Asyncrhonous USB Type-B Port: A rear-panel asynchronous
24-bit/192kHz USB (type-B) port enables the 851D to be connected to your Windows
PC or Mac computer. An asynchronous USB audio input means that the 851D acts as
a high quality external soundcard, allowing bit-perfect transfer from the
connected computer to the 851D,
ensuring all data is delivered in perfect timing for the highest possible sound
quality. The 851D supports USB 1.1 (Full-speed), USB 2.0 (Hi-Speed), USB 3.0
port-types. The 851D also supports USB protocols 1.0 and 2.0, which are
different than USB port-types.
- PC Compatible: With the 851D switched to USB Audio
(this is the default setting), the 851D will work with the native Windows
XP, Vista or 7 Audio 1.0 driver (no need to load any new driver) and accept
audio up to 24-bit/96kHz. With the 851D switched to USB Audio protocol 2.0, the 851D
needs the Cambridge Audio USB Audio 2.0 Driver to be loaded and can then
accept up to 24-bit/192kHz (and support ASIO and WASAPI Exclusive if
- Mac Compatible: No extra drivers are required to
connect your Mac computer. With the 851D switched to USB Audio protocol 1.0, the
851D will work with the native Mac OS-X 10.5 (Leopard) or above Audio 1.0
driver and accept audio up to 24/96kHz. With the 851D switched to USB Audio
2.0, the unit works with the native Mac OS-X 10.5 (Leopard) or above Audio
2.0 driver and can accept audio up to 24/192kHz.
Note: A Ground Lift Switch enables the USB interface to be
disconnected from the 851D chassis ground Disconnecting (lifting) the ground
can be useful if electronic hum is heard through the speakers when the USB
input is selected. The switch should otherwise be left in the Ground
Digital Inputs/Outputs: The Cambridge Audio 851D is fitted with two coaxial
(RCA), four optical (toslink), one BNC coaxial, and one AES/EBU (XLR) inputs.
The DAC's digital inputs support two-channel PCM audio signals only. If you connect a
DVD player or similar device, please ensure that the audio output of the player
is set to two-channel PCM (not Dolby Digital/DTS). The coaxial, BNC, and AES/EBU
digital inputs support up to 16-24 bit, 32-192kHz audio signals. The optical
digital input only supports 16-24 bit, 32-96kHz audio signals. A rear-panel
digital optical and coaxial output allows pass-through of the selected
digital source for recording purposes (no up-sampling performed). These outputs
loop or pass-through unprocessed digital audio from the selected digital input.
Bluetooth Audio Streaming: Simply plug in the included BT100 Bluetooth
audio receiver into the 851D's rear-panel USB (type-A) port for wireless music
streaming from many of today's most popular Bluetooth supporting devices; such
as iPod touch/iPhone/iPad, Android smartphone/tablet, and Windows/Mac computer.
The BT100 even supports the high-quality Bluetooth aptX CODEC, so you can stream
audiophile quality music from your Bluetooth-enabled source device to the 851D.
Balanced & Unbalanced Analog Outputs: The Cambridge Audio 851D
features both unbalanced RCA and balanced XLR outputs. XLR is a higher-quality
output that can reject noise and interference when combined with high-end
equipment that offer balanced inputs. The 851D can be connected to Cambridge
Audio's 851E stereo preamplifier (779851EB,
sold separately) or other brand of preamplifier (sold separately). Because the
851D can also be used as a digital preamplifier, it can be connected directly to
Cambridge Audio's 851W power amplifier (779851WB,
sold separately) or other brand of amplifier (sold separately). Connected
directly to a power amp, the 851D can be used to control volume and balance
levels. This clever feature, processed completely using digital technology,
facilitates the simplest of audio replays systems and offers amazing
flexibility. This function is operated using Blackfin DSP (Digital signal
Processor) and gives the highest quality of digital volume control, as opposed
to analog attenuation or digital bit reduction.
Headphone Amp: The Cambridge Audio 851D features a
built-in, low distortion headphone amp with a front-panel 1/4" headphone jack to
connect a pair of headphones. When headphones are connected, the other analog
outputs are muted. Use headphones with an impedance of 12 to 600 ohms.
All-Metal Chassis: The 851D features a full metal casework design with
thick brushed aluminum front panel and dual layer damped feet, giving enhanced
Front-Panel LCD: The 851D has a front-panel display that
shows the current status and allows you to access the 851D' system settings
menu. Here you can adjust the listening settings of the DAC to your personal
preference. The menu system is easy to navigate and control from the remote or
DAC. You can adjust the brightness of the display.
IR Remote: The 851D is supplied with an IR remote control
that wirelessly operates this DAC, as well as other Cambridge Audio 851 series
products and Stream Magic gear (sold separately).
Remote Control Inputs: The 12V trigger output (3.5mm) can be used to
control external devices such as an 851W or another power amplifier, or a
subwoofer, projector, screen etc. The 851D also features a IR Emitter input
(3.5mm) which allows modulated IR commands from multi-room systems or IR
repeater system to be received by the DAC. In addition, the 851D features a
Control Bus Input & Output (RCA), which allows un-modulated commands from
multi-room systems or other components to be received by the DAC and loop out to
another unit. The 851D's RS232 port is used for control of the DAC in custom
install situations from an external controller
Auto Power Down: The 851D will power down after 30, 60, or
120 minutes of inactivity. This feature can also be turned off.